Octopus: A fault-tolerant and efficient ad-hoc routing protocol

Mobile ad-hoc networks (MANETs) are failure-prone environments; it is common for mobile wireless nodes to intermittently disconnect from the network, e.g., due to signal blockage. This paper focuses on withstanding such failures in large MANETs: we present Octopus, a fault-tolerant and efficient position-based routing protocol. Fault-tolerance is achieved by employing redundancy, i.e., storing the location of each node at many other nodes, and by keeping frequently refreshed soft state. At the same time, Octopus achieves a low location update overhead by employing a novel aggregation technique, whereby a single packet updates the location of many nodes at many other nodes. Octopus is highly scalable: for a fixed node density, the number of location update packets sent does not grow with the network size. And when the density increases, the overhead drops. Thorough empirical evaluation using the ns2 simulator with up to 675 mobile nodes shows that Octopus achieves excellent fault-tolerance at a modest overhead: when all nodes intermittently disconnect and reconnect, Octopus achieves the same high reliability as when all nodes are constantly up. A preliminary version of this paper appears in Proceedings of the 24th IEEE Symposium on Reliable Distributed Systems (SRDS 2005) October 26–28, 2005, Orlando, Florida. Idit Keidar is a faculty member at the department of Electrical Engineering at the Technion Israel Institute of Technology, and a recipient of the national Alon Fellowship for new faculty members. She holds Ph.D., M.Sc. (summa cum laude), and B.Sc (summa cum laude) degrees from the Hebrew University of Jerusalem. She was a postdoctoral research associate at MIT’s laboratory for Computer Science, where she held post-doctoral fellowships from Rothschild Yad-Hanadiv and NSF CISE. Dr. Keidar has consulted for BBN Technologies (a Verizon Company) in the area of fault-tolerance and intrusion tolerance, and for Microsoft Research in the area of fault-tolerant storage systems. Dr. Keidar’s research focuses on reliability in distributed algorithms and system. She is the academic head of Software Systems Laboratory at the Technion. Dr. Keidar served as a member of the Steering Committee of the ACM Symposium on Principles of Distributed Computing (PODC), has served on numerous program committees of leading conferences in the area of distributed and parallel computing, has twice served as a vice-chair for the IEEE International Conference on Distributed Computing Systems (ICDCS), and once served as a vice-chair for Euro-Par. Yoav Barel is a Senior Business Line Manager at Sun Microsystems. He holds a B.Sc from the Technion—Israel Institute of Technology. Mr. Barel works with wireless carriers world wide and assists them in deploying innovative services based on cutting edge Java technologies. Roie Melamed is a research staff member at IBM Haifa Research Laboratory. He holds Ph.D. and B.A. (cum laude) degrees from the Technion—Israel Institute of Technology. Dr. Melamed’s research focuses on reliability in distributed systems.     

Selective Sampling Using the Query by Committee Algorithm

We analyze the query by committee algorithm, a method for filtering informative queries from a random stream of inputs. We show that if the two-member committee algorithm achieves information gain with positive lower bound, then the prediction error decreases exponentially with the number of queries. We show that, in particular, this exponential decrease holds for query learning of perceptrons.     

Shaped Charge Jet Tail Velocity

The impact of a shaped charge jet, created by a stationary charge onto a moving target, creates an elongated cut on the target face. The length of the cut, together with additional data about the charge and target configuration, enables the calculation of the jet tail velocity. It was found that this velocity increases with the stand-off distance between the charge and the target. A possible cause for this acceleration is that the jet material is under tension due to the velocity gradient along it and the stress throughout it equals the dynamic flow stress of the material. This stress pulls on the jet material towards the center of gravity and tends to reduce the velocity gradient, i.e. decelerate the tip and accelerate the tail. 1D simulations show that this mechanism results in a constant acceleration of the tail, and that the acceleration depends on the flow stress of the jet material, hence on its temperature. Based on the experimental evidence and on the simulations, it is postulated that in addition to the velocity gradient along the jet, there are temperature and strength gradients along it, as well.     

Imagined positive emotions and inhibitory control: The differentiated effect of pride versus happiness.

Inhibitory control is a cognitive mechanism that contributes to successful self-control (i.e., adherence to a long-term goal in the face of an interfering short-term goal). This research explored the effect of imagined positive emotional events on inhibition. The authors proposed that the influence of imagined emotions on inhibition depends on whether the considered emotion corresponds to the attainment of a long-term goal (i.e., pride) or a short-term goal (i.e., happiness). The authors predicted that in an antisaccade task that requires inhibition of a distractor, imagining a happiness-eliciting event is likely to harm inhibitory processes compared with imagining a pride-eliciting event, because the former but not the latter primes interfering short-term goals. The results showed that imagining a happiness-eliciting event decreased inhibition relative to imagining a pride-eliciting event. The results suggest a possible mechanism underlying the role of imagined positive emotions in pursuit of goals that require self-control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optothermophysical properties of demineralized human dental enamel determined using photothermally generated diffuse photon density and thermal-wave fields

Noninvasive dental diagnostics is a growing discipline since it has been established that early detection and quantification of tooth mineral loss can reverse caries lesions in their incipient state. A theoretical coupled diffuse photon density and thermal-wave model was developed and applied to photothermal radiometric frequency responses, fitted to experimental data using a multiparameter simplex downhill minimization algorithm for the extraction of optothermophysical properties from artificially demineralized human enamel. The aim of this study was to evaluate the reliability and robustness of the advanced fitting algorithm. The results showed a select group of optical and thermal transport parameters and thicknesses were reliably extracted from the computational fitting algorithm. Theoretically derived thicknesses were accurately predicted, within about 20% error, while the estimated error in the optical and thermal property evaluation was within the values determined from early studies using destructive analyses. The high fidelity of the theoretical model illustrates its efficacy, reliability, and applicability toward the nondestructive characterization of depthwise inhomogeneous sound enamel and complex enamel caries lesions.     

Superhydrophobic Graphene Foams

The static and dynamic wetting properties of a 3D graphene foam network are reported. The foam is synthesized using template‐directed chemical vapor deposition and contains pores several hundred micrometers in dimension while the walls of the foam comprise few‐layer graphene sheets that are coated with Teflon. Water contact angle measurements reveal that the foam is superhydrophobic with an advancing contact angle of ～163 degrees while the receding contact angle is ～143 degrees. The extremely water repellent nature of the foam is also confirmed when impacting water droplets are able to completely rebound from the surface. Such superhydrophobic graphene foams show potential in a variety of applications ranging from anti‐sticking and self‐cleaning to anti‐corrosion and low‐friction coatings.     

Negotiation as a form of persuasion: Arguments in first offers.

In this article we examined aspects of negotiation within a persuasion framework. Specifically, we investigated how the provision of arguments that justified the first offer in a negotiation affected the behavior of the parties, namely, how it influenced counteroffers and settlement prices. In a series of 4 experiments and 2 pilot studies, we demonstrated that when the generation of counterarguments was easy, negotiators who did not add arguments to their first offers achieved superior results compared with negotiators who used arguments to justify their first offer. We hypothesized and provided evidence that adding arguments to a first offer was likely to cause the responding party to search for counterarguments, and this, in turn, led him or her to present counteroffers that were further away from the first offer. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Mangrove health in an arid environment encroached by urban development--a case study

Urban development will soon encroach upon several protected and largely unspoiled arid climate mangroves ecosystems located along the lagoon called Ensenada de La Paz in Baja California Sur, Mexico. Many of these mangroves are located on a large sandbar that separates the lagoon on the south side from Bahía de La Paz to the north. A general evaluation of the current status of these mangroves was conducted to establish biological and physicochemical indicators of the health of these mangroves to serve as a natural or predevelopment baseline in future management. The following parameters were measured in the feeding channels of the mangroves and at the mouth of the channels: vegetation coverage, species and health, and levels of dissolved oxygen, pH, salinity, total nitrogen, ammonium, nitrates and nitrites, phosphorus ions, and organic matter in sediments and seawater. The microbiological elements that were studied included aerobic bacteria, N2-fixing bacteria, inorganic phosphate solubilizers, coliform, and phytoplankton diversity. Bird populations were counted, with special attention to migratory and resident birds and protected and endangered species. A comprehensive analysis of all the elements indicated that the health of the sandbar mangrove populations is good despite the proximity of a modest urban center. It also demonstrated that several biological and physicochemical parameters used in this study, including the birds, can serve as indicators of mangrove health and as a baseline for future management of mangroves in regions with arid climates.     

Scheduling a system of nonsingular affine recurrence equations onto a processor array

Most work on the problem of scheduling computations onto a systolic array is restricted to systems of uniform recurrence equations. In this paper, this restriction is relaxed to include systems of affine recurrence equations. In this broader class, a sufficient condition is given for the system to be computable. Necessary and sufficient conditions are given for the existence of an affine schedule, along with a procedure that constructs the schedule vector, when one exists. This material is based upon work supported by the Office of Naval Research under contract nos. N00014-84-K-0664 and N00014-85-K-0553.